Tetra Tech, Inc.

10306 Eaton Place, Suite 340 Fairfax, VA 22030 phone 703
- 385
- 6000 fax 703
- 385
- 6007

DATE: December 8, 2008 TO : Paul Shriner, EPA FROM : Kelly

Meadows, SUBJECT: Analy sis of swim speed data Tetra Tech was tasked with researching 0.5 feet per second (fps) threshold for fish swim speed in impingement mortality

in the 3 treatment of swim speed in the previous rules, as well as provide the development of the revised Background Impingement is generall y correlated to three factors: swim speed. 1 The latter two factors are closel y related, as the ability of fish to evade impingement depends on the swimming ability of the individual fish and the intake velocity against which it is attempting to e regulating the intake velocity at cooling water intake structures way to minimize impingement impacts. Where to Measure Intake Velocity Intake velocit y can be measured at a number of loc significant impact on the effectiveness of the

 Far

- field: Measured at a large distance from the intake structure. T area of effect of an intake structure dissipates over a relatively small become lost in ambient currents in the waterbod y be a useful metric for reducing impingement.

1 See 69 FR 41612. In contrast, entrainment is generally related only 

### MEMORANDUM
10306 Eaton Place, Suite 340

December 8, 2008 Paul Shriner, EPA Kelly Meadows, Tetra Tech Analy sis of swim speed data Tetra Tech was tasked with researching the origins of (and continued applicability of) the 0.5 feet per second (fps) threshold for fish swim speed in reducing impingement and the 3 16(b) regulations. The sections below discuss the in the previous rules, as well as provide discussion to consider in revised Phase I I rule.

Impingement is generall y correlated to three factors: intake flow, intake velocity , and fish

The latter two factors are closel y related, as the ability of fish to evade impingement depends on the swimming ability of the individual fish and the intake velocity against which it is attempting to e scape. EPA has consistently recognized that regulating the intake velocity at cooling water intake structures (CWIS) is an effective way to minimize impingement impacts. Where to Measure Intake Velocity Intake velocit y can be measured at a number of loc ations, each of which can have a significant impact on the effectiveness of the velocity threshold : Measured at a large distance from the intake structure. T ypicall y, the effect of an intake structure dissipates over a relatively small distance become lost in ambient currents in the waterbod y . Far

- field velocit y is unlikely to be a useful metric for reducing impingement.

See 69 FR 41612. In contrast, entrainment is generally related only to intake flow

. 1 the origins of (and continued applicability of) the reducing impingement and The sections below discuss the to consider in

intake flow, intake velocity , and fish The latter two factors are closel y related, as the ability of fish to evade impingement depends on the swimming ability of the individual fish and the intake scape. EPA has consistently recognized that is an effective

ations, each of which can have a

ypicall y, the distance , as it field velocit y is unlikely to2

 Approach velocity : M easured at some distance in front of the screen (often defined as a few inches [EPRI2000] ) , just at or before the point where velocities increase before passing through the screen

.  Through

- screen : Measured in the open area of the screen, as water and organisms pass through. Through

- screen velocit y has been EPA’s preferred metric for the Phase I, II, and III rulemakings.
I ntake velocit y measurements should be measured at the “first point of contact,” where an organisms would be presented with the first (and perhaps best ) opportunity to detect the intake structure and avoid it . For example, a facility that employ s an intake canal should measure the intake velocity at the mouth of the canal, as organisms can detect the intake and avoid the canal. If the intake velocit y was measured at the intake screen (and not the mouth of the canal), organism s may be drawn into the canal but be unable to return to the primary waterbod y and may eventuall y be impinged. Adding numbers to this example, a facility with an intake canal has an intake velocit y of 1.0 fps at the mouth of the canal and 0.5 fps at its traveling screens near the facility . In this case, organisms are not provided with the optimal opportunity to avoid being impinged, as they

may be drawn into the canal due to the higher intake velocity . Once in the canal, escape may

be difficult and the o rganism may eventuall y be impinged, despite the lower intake velocity

at the screen itself. Another example would be a facility with an offshore intake structure that supplies cooling water to an onshore forebay . The intake velocity should be measured at the offshore intake structure, as an organism drawn into the CWI S and forebay would have no chance of escape (except possibly through a fish return ; however, survival rates for organisms passing through a fish return is often low ). Similarly , measuring the velocity of flow in the conduits behind the screen is not ap propriate, as an y organism behind the screen will not have an opportunity to escape. 2 Other Biological Factors Affecting the Swim Speed Threshold Two other biological factors can also affect the ability of fish to escape an intake structure. EPA’s approach to account for these factors is also discussed

.

 Horizontal versus vertical flow vectors: Fish are generall y unable to detect changes in flow or velocity in a vertical direction. A ny intake that withdraws water verticall y (e.g., an uncapped offshore intake) poses a significant impingement hazard. o A ll intake velocity

measurements should be measured in the horizontal direction.

 Categories of swim speed: Fish ty picall y exhibit two general ty pes of swimming

—

prolonged continuous swimming or burst swimming (EPRI2000)

. The former is the most common and is slower. Burst swimming is usually

2 In fact, some intake systems are designed to have high (>3

- 5 fps) velocities behind the screens, as this can inhibit the colonization of fouling organisms.3 induced b y an outside stimulus (e.g., chasing prey, escaping a disturbance) and is much higher, but ty

pica lly the organisms only travel a short distance. o B urst swim speeds are higher and may provide fish with an improved ability to react to stimuli (including intake screens) . However, even with short periods of burst swimming, a fish may avoid initial contact with the screen but may

be unable to eventually

escape the area of the intake structure. As such, EPA ’s conservative approach of using swim continuous/prolonged swimming speeds in its analysis is appropriate

. Phase I Rule The Phase I rule established r equirements for all new intakes to have a maximum design intake velocit y of 0.5 fps. 3 The final rule describes the anal ys is EPA used: precedent from previous Federal studies, existing data, and an anal ys is of fish length versus swim speed. (See 66 FR 6527 4.) The information collected indicated that a 0.5 fps threshold would be protective of 96% of the species and life stages found in the data

. In addition, the Electric Power Research Institute (EPRI ) submitted a 2000 study with its comments on the Phase I Notice of Data Availability (NODA) titled “Technical evaluation of the utility

of intake approach velocity as an indicator of potential adverse environmental impact under Clean Water Act Section 316(b).” This compreh ensive review of swim speed literature contained most of the data used b y EPA in justifying the 0.5 fps threshold. EPRIagreed that intake velocity was an appropriate regulatory criterion, and that while it preferred a site

- specific approach to setting in take velocit y limits, that a limit of 0.5 fps was a useful threshold for screening out significant impingement events at CWI S s . In the NODA and in a memo to the record, 4 EPA discussed the intake velocities at existing facilities, noting that most facilities constructed in the last 15 y ears alread y meet th e 0.5 fps threshold. EPA’s intake velocit y threshold was challenged in litigation but was upheld by the Second Circuit

. Phase II and Phase III Rule s The 2004 Phase II rule used the same data, anal ys es and conclusions presented in Phase I to support a compliance alternative where an intake at a facility with a design through

screen velocit y of 0.5 fps meets the impingeme nt requirements. Similarly , the proposed Phase III rule utilized the same regulatory framework as the Phase II rule, including the 0.5 fps intake velocit y threshold. In the final Phase III rule, EPA opted not to regulate land

- based facilities, but continued to impose the intake velocit y requirements on certain offshore facilities. 5

3 See 128.84(b)(2) and (c)(1). 4 See 66 FR 28864 and DCN 2

- 030, respectively. 5 S ee 125.134(b)(2).4

Revised Phase II R

ule In response to the Second Circuit decision, EPA is revising the Phase II rule. As part of this rulemaking, EPA opted to briefl y re - examine the basis f or the 0.5 fps threshold, as well as conduct additional screening anal ys es. In review ing the swim speed data in the record , the previous conclusions continue to be supported by

the data

. First, man y intakes already meet this standard, thereb y reducing the burden of meeting the requirement. 6 In fact, many intake technologies installed today (e.g., cy lindrical wedgewire screens) are specificall y designed to meet the 0.5 fps threshold. Second, as described above, a 0.5 ft/sec through

- screen velocit y would be protective of 96% of species. It is possible that a lower intake threshold may be appropriate under certain conditions (e.g., Alaska’s limits to protect salmonids 7 ) ; however, on a p ractical level, it is likely not appropriate to set a threshold lower than 0.5 fps on a national level. 8 Some have argued that the data on intake velocity and fish swim speed support a higher threshold (up to 1.0 fps), but it should be reco gnized that int ake screens rarely operate at optimal conditions. Given the potential for screen clogging and debris loading (which would reduce the open area of the screen and increase the through

- screen velocity even further), the 0.5 fps threshold also provides for an appropriate safet y margin for aquatic organisms. Analy ses were conducted to determine if the velocity threshold should v ary

by waterbod y ty pe. T he swim speed data from the EPRIreport was plotted by fish assemblage, a categorization of fish species by w aterbody

ty pe (e.g., Pacific Ocean, rivers in the Eastern U.S., etc.). (See attached.) These plots did not show an y clear differentiation of swimming ability

between fish in the various waterbodies nor did an y waterbody t ype appear to be an y more vulnerab le than another ; it is therefore reasonable to conclude that the 0.5 fps national intake velocit y limit is appropriate for all waterbod y t ypes.

6 According to data from EPA’s 2000 industry questionnaire, approximately 18% of intake structures meet the 0.5 fps threshold. Another 21% are less than 1.0 fps. See DCN 4

- 4023C “ Preliminary Data Analyses Using Responses from the Detail ed Industry Questionnaire: Phase II Cooling Water Intake Structures (Draft) .” 7 See attached and DCNs 2

- 028A through D in the Phase I docket. 8 The incremental increase in organisms protected w ould not be w ell

- balanced against the significant increase in costs for expanded screen area.5

References Alaska Department of Fish and Game (ADF&G). 1998. Water Intake Structures: an Alternative to Traditional Screened

- Box Enclosures for the Protection of Fish. Prepared by Robert F. “Mac” Mclean for the ADF&G Habitat and Restoration Division. March 20, 1998. Technical Report 97

- 8. Electric Power Rese arch Institute (EPRI). 2000. Technical Evaluation of the Utility of Intake Approach Velocity as an Indicator of Potential Adverse Environmental Impact under Clean Water Act Section 316(b). EPRI, Palo Alto, CA. 1000731. Environmental Protection Agency (EPA ). 200 1

. Preliminary Data Anal ys es Using Responses from the Detailed Industry Questionnaire: Phase II Cooling Water Intake Structures (Draft) . DCN 4

- 4023C.